SAM collections illuminate
Indigenous Australians use ochre to add colour and detail to items such as this shield at the South Australian Museum. Image courtesy of South Australian Museum, Author provided.
Rachel S. Popelka-Filcoff, When bacteria tell a story: tracing Indigenous Australian ochre sources via microbial ‘fingerprinting’, The Conversation, 20 October 2017
We have found a new method for pinpointing the geological origins of ochre found in Indigenous Australian artefacts.
The technique relies on RNA (a form of genetic material) from soil microbes to identify the ochre source.
This provides a fresh approach to understanding the inherent “fingerprint” of the origins of the natural pigment, and a new tool in the kit for the analysis of archaeological materials.
It can help us look back in time to see from where ochre was sourced, and how it may have been exchanged by Indigenous Australians.
The complexity of ochre
Natural mineral pigments such as ochre are the palette of cultural expression for Indigenous Australians, from when their forebears first arrived on this continent, and still today.
The intense colours stand the test of time for illuminating traditions. Although universally used across Australia, the minerals are obtained from specific, culturally significant locations. These pigments were exchanged across the continent as part of cultural exchangeover many thousands of years.
Ochre itself is a complex chemical mixture of minerals, ores and weathered materials that are representative of its genesis and history.
But similar to other soils and geological materials, ochre also contains once-living, or still alive components, such as bacteria, fungi and plants.
All of these microorganisms are a source of genetic materials such as DNA and RNA: together, they generate a rich data set to compare and identify ochre samples. The pattern of biological components in ochre reflects the genesis and history of that ochre.
Ochre trading routes
In the case of Indigenous natural mineral pigments, records that describe the first points of interaction between Europeans and Indigenous Australians document extensive cultural exchange in ochre along established routes. In some cases, these were known to extend hundreds of kilometres.
Regardless of whether these routes were relatively local or across the continent, the majority of them are now lost post-European contact. In addition to material exchange of pigments and other materials, these exchange networks promoted interchange of cultural networks and communities, and are an important part of Indigenous Australian culture.
Similarly to a forensic investigation, advanced archaeological science methods can be used to uncover the original “fingerprint” and therefore the original source of the raw materials, and potentially reconstruct these exchange networks lost to history.
Previously, we have used several techniques aimed at identifying where ochre originated based on the chemical and physical fingerprint of the material. These include analysis of elements such as arsenic, zinc, and antimony (known as trace elements), composition of minerals in the iron oxide, and mapping out the patterns of composition of different ochres.
For this study we demonstrated in a proof of concept that analysis of microbe RNA, a form of genetic material, can be used to discriminate between samples from four known ochre sites. This profiling can be used to identify a particular ochre material.